Simple heat pumps have been in use in a wide variety of applications, typically as being so called air conditioners, for cooling a building during hot months. The typical air conditioner collects heat from air circulating inside the building, transfers the heat to air circulating outside the building, and thereby cools the interior of the building.
In most of these applications air within the building is simply circulated back into the building. Air outside the building is simply circulated back into the outside atmosphere.
Similarly, heat pumps are used in reverse. Thus heat may be collected from the air outside the building, and transferred to air within the building. In these applications again, air outside the building is simply cycled through a heat pump outside the building and returned to atmosphere. Air within the building is cycled through a heating coil within the building, and returned to the building atmosphere.
In both applications, the actual heat transfer takes place from the outside of the building to the inside of the building, or vice versa, by outside coils physically located outside the building, and inside coils located inside the building.
The inside and outside coils are of course connected by pipes or conduits, and a suitable compressor maintains circulation.
A refrigerant, typically "Freon" (Trade Mark) gas or the like passes through the coils, and physically carries the heat from outside the building to inside, or from the inside to the outside, transferring it from one set of coils to another, via the conduits, and pipes.
These systems have inherent inefficiencies.
In heat exchanger technology, it is well known that the efficiency is proportional to the temperature difference. When it is attempted to operate a heat pump, to collect heat outside the building and transfer it into the building, the efficiency drops substantially as the temperature of the outside air drops. This produces a loss in efficiency at the time of the greatest need for heat input into the building.
The efficiency of an air conditioner will also depend on the temperature of the outside air. As this outside air temperature rises, the efficiency of heat rejection to the atmosphere diminishes, just at the point when the greatest load is placed on the equipment, due to the need for removing heat from the inside of the building.
In spite of these problems however air conditioners are in very wide use, and heat pump technology for recovering heat from the outside air is gaining increasing acceptance. Dual installations, where a single heat exchanger system is used for both functions, are becoming popular.
In fact however due to the loss of efficiency especially in the heat pump cycle, the actual savings in heating costs in the building are quite small.
Domestic heat pumps usually do not operate below a certain preset outside temperature.
An additional factor which must be included in such an equation is the cost of the equipment, and the cost of servicing and replacement.
Heat pumps of all kinds operate most efficiently when they are operated at a fairly stable cycle, and over a predetermined stable temperature range.
Thus for example in the normal household refrigerator, which operates in a very narrow temperature range, it is common for refrigerators to have a useful life up to twenty years.
Household air conditioners such as central air conditioners operate over a much wider temperature range than for example a refrigerator. However the temperature range is relatively stable, and given suitable engineering it is possible to make such a central air conditioning unit have a useful life of up to twenty years.
However, when it is attempted to combine the air conditioning function with a heat pump function, it becomes apparent that the unit will be forced to operate over a very much wider temperature range from say 100.degree. F. in high summer, to -10.degree. F. in winter.
The problems of engineering such a heat pump having such a very broad operating range become much greater. As a result, it is found that the useful life of a combination air conditioner/heat pump installation may well be reduced.
When the cost of replacing this equipment is added to the overall cost equation, it will become apparent that there is in fact little or no saving achieved when using a heat pump, as compared with conventional heating.
In addition to these factors is that in fact the operation both of an air conditioner and a heat pump involve very substantial losses in waste heat.
In the case of the air conditioning cycle, electrical energy is being used to dump heat outside the building, and to circulate large volumes of hot, outside air, through the heat exchanger.
In the heat pump cycle substantial electrical energy is being used to transfer heat from the outside of the building to the inside, and to circulate large volumes of cold outside air through the collector coils outside the building. In addition, a defrost cycle is used in most heat pumps.
The typical household, in addition to requiring air conditioning, in summer and air heating in winter, also requires a supply of domestic hot water. In the typical household hot water is supplied by an electrically powered hot water tank.
This represents additional expense in power consumption. Clearly it is desirable that, whenever possible, excess heat in the building shall be used for heating water, to reduce power consumption for this purpose, at least during the warmer months.
Clearly, it is desirable to provide a heat recirculating apparatus capable of operating both a cooling and a heating cycle, and in which the operating temperature range is greatly reduced, so as to provide a unit having a longer working life and reduce the stresses due to extreme temperature variations, and in which, at the same time, to a large extent the energy values inherent in the operation of the unit are recovered.
For example, during summertime operation at least, it is desirable that some of the heat being rejected to the outside by the operation of the unit, may be recovered and used to heat the domestic hot water supply. This will also reduce the load on the heat exchangers and compressor.
In addition to all of these problems, which are directed solely to the efficiency of heating and cooling the interior of the building such as a home, or the like, is the entirely different problem of maintaining a healthy atmosphere within the building.
Present day domestic air circulating systems make no provision whatever for the venting of stale air to atmosphere, or for the introduction of fresh air from outside.
Domestic construction simply assumes that fresh air will continuously percolate into the building through various cracks, and that stale air will be dissipated in the same way.
As energy costs continuously increase, householders constantly seek ways to improve the thermal insulation of their homes. This includes both additional straight-forward insulation in walls, ceilings, windows and the like, but more importantly, it includes more efficient ways of closing cracks and openings in the building. In fact, there are numerous instances of insulation being installed so effectively that the operation of a fossil fuel furnace such as an oil or gas furnace in the home, become inefficient and even dangerous. Cases have arisen where occupiers of a home have in fact been injured or even killed by the accumulation of exhaust fumes and the like from furnaces, caused by incomplete combustion. Clearly, it is obvious that the greater the efficiency of the air percolation barriers in the building, the greater will be the likelihood of problems related to the lack of fresh air.
It is therefore desirable if in the design and construction of a heat recirculating unit of the type described, provision can be made for the continuous venting of a proportion of the building atmosphere, from the inside to the outside of the building, and the continuous introduction of fresh air from the outside, to maintain a fresh healthy atmosphere within the building.
The use of fossil fuels within the home or building may also be eliminated by the use of the unit according to the invention.
In accordance with the invention, all of these objectives are achieved simultaneously in a single unit which both heats and cools the interior of the building in accordance with seasonal requirements, and which also provides a large measure of heat recovery for heating the domestic hot water system, and which also continuously ejects stale air, after extraction of its heating values, introduces fresh air, in an efficient manner producing substantial savings of energy, and which may also recover heat from geothermal sources.